Factorial design in optimization of PHAs processing

Poly(hydroxyalkanoate)s (PHA)s, as all melt-processed polymers, may undergo thermal degradation at temperatures close to the melting point. The primary purpose of the present study is to screen out process variables on the basis of a factorial design for two variables at two levels. The investigated parameters for PHA polymer samples processed in a torque rheometer were structure of PHA, processing temperature, and rotor speed. For polymers processed by compression molding, only the first two variables were considered and purification. The main effects and possible interactions were verified by the changes of molecular weight and thermal properties, as detected by DSC and TGA. It was observed that molecular weight decreased up to about 50% while the thermal properties did not appreciably change.     

Simultaneous Quantification of 25 Fentanyl Derivatives and Metabolites in Oral Fluid by Means of Microextraction on Packed Sorbent and LC–HRMS/MS Analysis

Fentanyl and fentalogs’ intake as drugs of abuse is experiencing a great increase in recent years. For this reason, there are more and more cases in which it is important to recognize and quantify these molecules and related metabolites in biological matrices. Oral fluid (OF) is often used to find out if a subject has recently used a psychoactive substance and if, therefore, the person is still under the effect of psychotropics. Given its difficulty in handling, good sample preparation and the development of instrumental methods for analysis are essential. In this work, an analytical method is proposed for the simultaneous determination of 25 analytes, including fentanyl, several derivatives and metabolites. OF was collected by means of passive drool; sample pretreatment was developed in order to be fast, simple and possibly semi-automated by exploiting microextraction on packed sorbent (MEPS). The analysis was performed by means of LC–HRMS/MS obtaining good identification and quantification of all the analytes in less than 10 min. The proposed method was fully validated according to the Scientific Working Group for Forensic Toxicology (SWGTOX) international guidelines. Good results were obtained in terms of recoveries, matrix effect and sensitivity, showing that this method could represent a useful tool in forensic toxicology. The presented method was successfully applied to the analysis of proficiency test samples.     

Mimicking Ziegler‐Natta Catalysts in Homogeneous Phase, 1. C2‐Symmetric Octahedral Zr(IV) Complexes with Tetradentate [ONNO]‐Type Ligands

Results of propene polymerization in the presence of two known octahedral C₂‐symmetric Zr complexes bearing tetradentate [ONNO]‐type ligands are reported for the first time. Depending on the steric hindrance at the active metal, isotactic site‐controlled or weakly syndiotactic chain‐end‐controlled polymers were obtained, in both cases via highly regioselective 1,2 (primary) monomer insertion. In this respect, the complexes mimic the behavior of the active Ti species on the surface of the heterogeneous Ziegler‐Natta catalysts of which they might represent good structural models.     

Structures and properties of lanthanide and actinide complexes by a new density functional approach: Lanthanum,gadolinium, lutetium,and thorium halides as case studies

The LaX₃, GdX₃, LuX₃, and ThX₄ systems (X = F, Cl, Br, and I) have been chosen as test cases to analyze the performances of a computational protocol, resting on a recently proposed density functional method, the so‐called PBE0 model. Relativistic effects were taken into account by means of two different sets of quasi‐relativistic effective core potentials. All static data were found to be in very good agreement with those provided by post‐HF methods. Because experimental geometries have been determined at high temperature (1000–1800 K), the effect of nuclear motions have been considered through a variational numerical procedure. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1153–1166, 2000     

Stick–slip oscillations in a multiphysics system

Nonlinear Dynamics - This work analyzes a multiphysics system with stick–slip oscillations. The system is composed of two subsystems that interact, a mechanical and an electromagnetic (a DC...     

A comparative study of phosphoric acid‐doped m‐PBI membranes

Phosphoric acid (PA)‐doped m‐polybenzimidazole (PBI) membranes used in high temperature fuel cells and hydrogen pumps were prepared by a conventional imbibing process and a sol–gel fabrication process. A comparative study was conducted to investigate the critical properties of PA doping levels, ionic conductivities, mechanical properties, and molecular ordering. This systematic study found that sol–gel PA‐doped m‐PBI membranes were able to absorb higher acid doping levels and to achieve higher ionic conductivities than conventionally imbibed membranes when treated in an equivalent manner. Even at similar acid loadings, the sol–gel membranes exhibited higher ionic conductivities. Heat treatment of conventionally imbibed membranes with ≤29 wt % solids caused a significant reduction in mechanical properties; conversely, sol–gel membranes exhibited an enhancement in mechanical properties. From X‐ray structural studies and atomistic simulations, both conventionally imbibed and sol–gel membranes exhibited d‐spacings of 3.5 and 4.6 Å, which were tentatively attributed to parallel ring stacking and staggered side‐to‐side packing, respectively, of the imidazole rings in these aromatic heterocyclic polymers. An anisotropic staggered side‐to‐side chain packing present in the conventional membranes may be related to the reduction in mechanical properties. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Polym. Phys. 2014 , 52, 26–35     

Random vibration of a point-driven two-span beam on an elastic foundation

In this study, we investigate the random vibrations of a point-driven two-span beam of length 2L on a linear elastic foundation. The normal mode approach is utilized. The natural frequencies are falling in two groups: the first group corresponds to the beam of length L that is simply supported at its ends; the second group is associated with the beam of length L that is simply supported at one end and clamped at the other end. The mean-square velocity of the beam is written in terms of auto- and cross-correlations within groups, as well as in terms of cross-correlations between the modes of two groups. In addition, the two-span beam experiences the clustering of frequencies with increased modal density. The effect of cross-correlations between the modal responses corresponding to closely spaced natural frequencies turns out to be extremely significant.